The present invention relates to a tapered roller bearing which is preferably used in an automotive pinion shaft supporting apparatus as in a differential and a transaxle and in a transmission of a vehicle or the like, and an automotive pinion shaft supporting apparatus which uses the tapered roller bearing.
In recent years, there has been increasing a demand for improvement in fuel economy of motor vehicles, and in association with the demand, there is expressed a desire to reduce the running torque of tapered roller bearings which are used to support rotational shafts of transmissions and differentials installed on those motor vehicles.
In these situations, as a method of reducing the running torque of a tapered roller bearing, there is a method of reducing the rolling friction of a tapered roller bearing by crowning rolling contact surfaces of tapered rollers and raceway surfaces of inner and outer rings.
As the method like this, as is described in Patent Document No. 1 below, there is proposed, for example, a method in which raceway surfaces are crowned in an arc-shape fashion so as to realize a reduction in running torque, or, as is described in Patent Document No. 2 below, there is also proposed a method in which rolling contact surfaces of rollers and raceway surfaces which are brought into contact therewith are crowned to a shape which approximates to a logarithmic curve.
In the conventional examples, the performance of the tapered roller bearing was attempted to be enhanced by specifying the shape of the crown imparted to the raceway surface or the rolling contact surface by a numerical value. However, there had been no attempt to grasp the crown as quantity so as to specify the crowning amount so imparted to thereby reduce the running torque of the tapered roller bearing.    Patent Document No. 1: JP-A-2003-130059    Patent Document No. 2: JP-A-2001-65574
Incidentally, by crowning the rolling contact surface or the raceway surface as described above, the running torque of the tapered roller bearing can be reduced but the contact pressure between the rolling contact surface and the raceway surfaces may be increased due to the bearing dimension and used condition. Therefore, the generation of abrasion of the contact surface and surface flaking become significant, thereby the life of the tapered roller bearing may be shorten. Due to this, there is a case that the main dimensions of the tapered roller bearing have to be relatively large in order to decrease the contact pressure, which leads a problem that further lowering torque and further downscaling are inhibited.
Especially, if the contact pressure between the rolling contact surface and the raceway surfaces is high, the generation of the surface flaking of the contact surface is accelerated due to the foreign matters such as abrasive powder of the gear being interposed between the rolling contact surface and the raceway surfaces, thereby a reduction in life of the tapered roller bearing becomes significant.